1. Technical Field
The present invention relates to wireless communications and, more particularly, to methods and systems for serving multi-mode communication devices.
2. Description of Related Art
In a cellular wireless communication system, a mobile station communicates over the air with a Radio Access Network (RAN) according to an air interface protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more specifications such as IS-95 and IS-2000. The RAN in turn provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and the Internet. To handle call setup, teardown, handoffs, and other functions, the mobile station and the RAN exchange CDMA signaling messages, such as IS-2000 signaling messages. Typically, the RAN is connected with a Mobile Switching Center (MSC), which in turn is connected with a signaling network such as a Signaling System 7 (SS7) network, over which the MSC signals with other switching points to perform call processing on behalf of the mobile station.
To place a call over the PSTN, for instance, the mobile station would, using IS-2000 as an exemplary CDMA protocol, send an IS-2000 origination message over the air to the RAN. That message or an equivalent in another protocol would then be transmitted to the MSC, providing the MSC with the calling and called numbers, among other data. The MSC would then engage in call-setup signaling, such as Integrated Services Digital Network (ISDN) User Part (ISUP) signaling, over the SS7 network, to set up the call via a switching point that serves the called party. When the called party answers, the MSC may then connect the call. Similarly, when the MSC receives a request to connect a call to the mobile station, it would typically cause the mobile station to be paged over the air, and, when the mobile station answers, connect the call. Both the paging and the call connection would typically involve IS-2000 messaging.
With the widespread growth of voice-over-IP (VoIP) technology, the industry has recently begun to introduce mobile stations—referred to herein as multi-mode devices—that are equipped to (i) operate in a CDMA mode, engaging in CDMA communications over a CDMA air interface with a RAN and (ii) operate in a Wi-Fi mode, engaging in VoIP communications in part over Wi-Fi with an access point. The VoIP communications associated with Wi-Fi mode are typically set up using Session Initiation Protocol (SIP) messaging between the device and a signaling gateway having an interface with a packet-based network and an interface with an SS7 network. The signaling gateway translates between SIP messages and SS7 messages to facilitate call processing over the SS7 network on behalf of the device.
For operation in these two modes, multi-mode devices typically include two substantially redundant, robust messaging modules: (1) a CDMA messaging module, for engaging in CDMA signaling with a RAN (when in CDMA mode) and (2) a SIP messaging module, for engaging in SIP signaling with a SIP/SS7 signaling gateway at least in part over Wi-Fi (when in Wi-Fi mode). Each messaging module must be capable of handling call setup, teardown, etc. Thus, where the CDMA messaging module would send, e.g., an IS-2000 origination message, the SIP messaging module may send a SIP INVITE message, and so on. Each of these messages would be complete according to their respective protocols, and contain all necessary data to carry out, in that example, a call-setup function. Development and maintenance of both of these messaging modules—as well as translation and other support on the network side—requires a significant investment of time, manpower, and other resources.